The present invention relates to a magnetoresistance effect type magnetic head apparatus.
A magnetoresistance effect type (hereinafter referred to as "MR") magnetic head apparatus has a magnetic head element h as shown in FIG. 12. On a magnetic substrate 1 of Ni-Zn ferrite or MN-Zn ferrite, or through an insulating layer 2 of SiO.sub.2 or the like on the substrate 1 if it is conductive, a bias conductor 3 is applied which provides a bias magnetic field generated by current passing therethrough to supply a bias magnetic field to a sensing element having the magnetoresistance effect (hereinafter referred to as "MR sensing element") as hereinafter described. The bias conductor 3 may be formed by a hand-shaped conductive film extending in one direction. An MR sensing element 5 comprising MR magnetic thin film of Ni-Fe alloys or NI-Co alloys is arranged over the bias conductor 3 on an insulation layer 4. A pair of magnetic layers 7 and 8 of Mo permalloy or the like as a magnetic core of a magnetic circuit are formed so that the magnetic layers 7 and 8 are positioned at each end over the MR sensing element 5 on a thin insulation layer 6, and extend across the bias conductor 3 and the MR sensing element 5. A protective substrate 10 is provided on the substrate 1 through a non-magnetic insulation protective layer 9. A front magnetic gap g is formed between one magnetic layer 7 and the front end of the substrate 1 through a non-magnetic gap spacer layer 11 comprising, for example, the insulating layer 6 having a required thickness. A front surface of the substrate 1, the gap spacer layer 11, the magnetic layer 7, the protective layer 9, and the protective substrate 10 are polished such that a surface 12 opposite a magnetic recording medium is formed, and wherein the magnetic gap g faces the medium. The rear end of the magnetic layer 7 which forms the magnetic gap g, and the front end of the other magnetic layer 8, are formed to ride on the MR sensing element 5 through the insulation layer 6, and both ends are spaced from each other by a discontinuous portion 13. The rear end of the magnetic layer 7 and the front end of the magnetic layer 8 are electrically insulated by interposition of the insulation layer 6 at both ends of the MR sensing element 5. They are, however, magnetically connected. The discontinuity portion 13 between both magnetic layers 7 and 8 is magnetically connected by the MR sensing element 5, so that a magnetic circuit is formed in a closed magnetic path around the substrate 1: the magnetic gap g - the magnetic layer 7 - the MR sensing element 5 - the magnetic layer 8 - the substrate 1.
In such a MR type magnetic head apparatus, a signal magnetic flux by a signal recorded on the magnetic recording medium flows from the magnetic gap g opposite the magnetic recording medium into the magnetic circuit. Thus a resistance value of the MR sensing element 5 in the magnetic circuit varies in response to the external magnetic field by the signal magnetic flux. Variation of the resistance value is detected as a voltage variation across the MR sensing element 5 and a sensing current i.sub.MR flows through the MR sensing element 5. Thus a reproduction of the recording signal on the magnetic recording medium is effected.
FIG. 13 shows a magnetoresistance characteristic curve of the MR sensing element. It is clear that the magnetoresistance characteristic curve of the MR sensing element 5 becomes a parabolic curve in a certain range of the magnetic field. Consequently, the sensitivity characteristics show a maximum value at two values of the magnetic field as shown in FIG. 14. A point of maximum sensitivity becomes also a point of good linearity. Consequently, in such a magnetic head, the bias magnetic field H.sub.B is applied with a nearly equal value to that supplying the maximum sensitivity to the MR sensing element 5. The bias magnetic field H.sub.B is supplied mainly by the external bias magnetic field H.sub.BO by a magnetic field induced by current flowing through the bias conductor 3. In actual practice, however, in addition to the magnetic field H.sub.BO, the bias magnetic field H.sub.B is supplied also by the magnetic field H.sub.MR generated by sensing current i.sub.MR flowing internally through the MR sensing element 5. In such an MR type magnetic head apparatus as clearly seen in a schematic diagram of FIG. 15, the MR sensing element 5 is supplied with the generated magnetic field, while prescribed d.c. current i.sub.BO flows through the bias conductor 3. At the same time, prescribed sensing current i.sub.MR flows through the MR sensing element 5. In such a state, the MR sensing element 5 is supplied with the bias magnetic field H.sub.B formed of the magnetic field H.sub.BO generated by energizing the bias conductor 3 and the magnetic field H.sub.MR generated by the sensing current i.sub.MR flowing through the MR sensing element 5, the signal magnetic field H.sub.s being applied from the magnetic recording medium. A voltage across the MR sensing element 5 on the basis of resistance variation by the signal magnetic field H.sub.s, i.e. a variation of potential at point A, is amplified by an amplifier 14 and detected at an output terminal 15. Numeral 16 designates a coupling capacitor.
In the MR type magnetic head apparatus as above described, the required bias magnetic field H.sub.B is applied to the MR sensing element. Thus, the working point is set with good sensitivity and linearity. However, if the magnetic head element in the MR type magnetic head apparatus is supplied with an undesirable external noise magnetic field H.sub.N other than the output magnetic field from the magnetic recording medium, for example a magnetic field generated from a motor or the like (hereinafter referred to as "external magnetic field"), a setting state of the magnetic field for the MR sensing element varies. Thus there is a variation of the sensitivity and linearity which causes generation of distortion and noise in the reproduction signal.
In the MR magnetic head element having characteristics as described in FIG. 13 and FIG. 14, if the external magnetic field H.sub.N of H.sub.N =0 (Oe), H.sub.N =+10 (Oe), H.sub.N =-10 (Oe) is applied to the band-shaped MR sensing element in the width direction, the sensitivity characteristic curves are as shown in FIG. 16. In FIG. 16, the sensitivity characteristic curve of H.sub.N =0 (Oe) does not pass through the origin, because, in addition to the magnetic field generated by current flowing through the bias conductor, i.e. the bias current i.sub.BO, the magnetic field H.sub.MR by the sensing current i.sub.MR flowing through the MR sensing element affects it.